Backup Power Generator

[Charles]

Hi

I live out on a remote farmhouse whose electric is supplied on overhead electricity poles.

In the two years that I have lived here, I've had about 20 power cuts. Some are only a few minutes and a nuisance, but others can last for a few hours.

I have lots of space outside, and a space ready for a power generator (petrol/deisel etc).

I have a couple of questions though.

- How do I calculate the power (watts) that an appliance requires?

- Is there a device that can measure the power requirement for an appliance, or for my entire power requirement (I have an economy 7 dual dial meter)

- When my power is initially connected after a power outage, all of the outside floodlights come on and create an initial surge. How would a generator cope with that?

I am assuming that once I have worked out my power requirement, I will need to find a generator large enough to cope with it.

I would be happy if the generator would power a lighting circuit, and maybe a few appliances (heating pump, boiler, television, radio etc).

Any experience/tips/advice would be greatly appreciated. Thanks

Charles

[Andy Dingley]

Post this to uk.rec.engines.stationary _Lots_ of experience in there.

[Mike]

We have the same blackout problems on our farm and have been looking for a suitable generator as well. I really wouldn't try to have a generator that can handle the whole house though. This requires some form of switchover between the systems which has to be reliable.

Instead we intended to put a number of clearly labelled sockets from the generator around the house so that they can be used as needed, plus some dedicated lights. The freezer and heating system (boiler/pump/valves) will be driven through battery backup UPSes so these will switch automatically and keep going for a couple of hours. If you want other electronic devices (TV. computer, etc) I would do the same for these rather than driving them from a generator which can be spikey.

>

[Ian Stirling]

It depends what you want.

The cheapest option is a small generator that you plug stuff into. The best option would be a UPS, which can take power from either the mains, or the generator, and will provide instant recovery from failure.

A relatively easy way would be a small UPS plugged into a socket on a ring.

Add another socket for the generator output.

From the UPS output, run a ring, from which are a few low-power (round 2A?) sockets, and lighting (not exterior security lights).

Plug TV/... into these.

If power-cut happens, then after a few minutes, you unplug the UPS and pilug it into the generator, then turn it on. A "proper" solution would use a transfer relay to automate the transfer, and some means of automatically starting the generator.

[Dave Liquorice]

UPS's are great for preventing your computer(s) throwing a wobbly with the short ones.

Take a look on eBay, the biggest up there ATM is 800kVA, comes in an acoustic container with arctic trailer base. 5 figure price tag though and fuel might run a bit expensive but you could flog the excess to the surrounding villages...

Look at it's rating plate. But be aware that things with motors need 2 or 3 times the rating to start, especially induction motors (fridges, freezers etc)

Maplin and Machine Mart have plugin power meters. The Maplin one seemed to get good reports recently (in here? try google).

How is space heating achieved, electric storage, oil, gas, other? I'd forget about trying to run storage heaters of a genny as the size of genny required would be rather large compared to your base load. Better to find an alternative emergency heat source, wood burner, portable gas fire or similar.

Things with motors probably give a bigger surge unless you have several kilowatt of external lighting. The easy solution to the to these surges is to pull the fuses or trip the MCBs them whilst starting up on genny. Then put the required ones back in one by one letting the genny recover between switch ons.

Don't forget the freezers/fridges... Assuming that that "lighting circuit" doesn't include you 10kW of exterior floodlighting then a smallish 3 to 4kVA generator should cope with all that load fairly easily.

Do take care of how you connect it into the house. Not only does it have to be totally fail safe in disconnecting the incoming mains when you are generator but you also need to think about earthing requirements. The former to stop you electricuting some poor linesman fixing the original fault. The latter so that you installation remains safe but how you achieve that varies on how you normal "mains" earth is derived.

Google is your friend, there have been many and long discussions in here on this subject in the past.

[bigcat]

normally theyre marked. With the odd item that isnt, if you dont have the ability to figure it out, use a power measuring meter such as the 'kilawatt' or similar.

But with gens its the VA that counts, not the W. Motors normally have both W and VA marked on the ratings plate. VA is larger than W for some goods, especially motors and fluorescent lights.

how many lights? of what type? What genny rating? What other loads?

The only way gennies can cope with big surges is to drop speed right down and either pick up again slowly or stall, depending on the nature of the load.

Best option is to avoid surge loading the thing, there are a number of ways to do this. But in your case, is the surge a problem for the genny to begin with?

Possibly, or you'll swear and decide to drop your load expectations.

Having run on 2 generators before, I'd say that trying to run them at max ratings is a real mistake. Both must have dropped to less than half speed under full load, making the nameplate ratings distinctly optimistic. Yeah sure, it _can_ put out 30A... at about 100v. Really we never got anything like rated output from either of them. I didnt know squat about engines at the time though.

Beware of putting TVs on gens, they tend to not survive. UPS much better there - or more realistically, just dont bother.

Gens produce large surges when loads are switched off, and such surges can kill electronic goods.

Radios can power themselves if fitted with rechargeable batteries plus a diode/resistor so the batteries charge automatically.

NT